I'm a big fan of this pet. I use him as an opener against the Thundering Spirit Tamer. I use Spiked Skin, Posioned Fang, and Powerball. The combo is great against the opening spirit beast. I've not used him in too many other situations yet, but I went from dreading that tamer fight to taking it as a given once I added this guy to the line up.

BTW: I generally follow him with a s/s snake and then finish off with anything tanky.

I've found that my Quilrat pup is one of my fave battlers. A combo of a poison skill, protect & damage skill, and a a fairly high damage & speed increase skill (that doesn't have a cooldown) is pretty powerful. I highly recomend it.